The proposed research program utilizes spectroscopic methods such as nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy and infrared spectroscopy to investigate interactions between enzymes and their substrates or metabolites which regulate the catalytic activities of the enzymes. The objective of the research is to determine structures of complexes formed between the enzymes and substrates or effector molecules in order to elucidate the mechanism of the respective catalytic reactions and of the factors which control or regulate the metabolic activities. Several classes of enzymes are under investigation including phospholipase A2 from mammalian pancreas, an enzyme which catalyzes degradation of phospholipid molecules, and various enzymes which involve transfer of phosphoryl groups in their catalytic reactions. All of the enzymes under investigation are activated by inorganic cations and the mechanistic roles of these cations are being examined.